I plan to examine the cellular basis of a simple example of associative learning, the initiation of locomotor behavior in the marine mollusk Hermissenda crassicornis. The motor system that controls locomotion will be studied using anatomical and cellular neurophysiological techniques. A functional mapping of light responsive motorneurons and interneurons will be carried out with cell staining techniques such as cobalt backfilling and the intracellular injection of HRP. The light responsive identified neurons will be studied following modification of the initiation of locomotion in a semi-intact preparation. The development of a semi-intact preparation will involve the use of behavioral, neurophysiological, and anatomical techniques. The cellular basis of a previously identified sensory neural correlate of associative learning will be examined with neurophysiological approaches. Basic mechanisms of visual excitation will be studied by focusing on changes in the characteristics of light-evoked discrete waves following conditioning. Voltage clamp experiments will be conducted to examine changes in light-induced membrane current in identified photoreceptors of Hermissenda following associative learning. The studies of the motor system will add to the already well-documented sensory network, and will provide a model system to study mechanisms of learning. The network would be amenable to a cellular analysis from the primary sensory neurons through the motor neurons that innervate the behavioral response. This identified system will be useful for studying the effects of pharmacological agents on learning and memory. Pertubations of the basic cellular functions of the system would be useful for studies of synaptic physiology of learning disorders that are relevant to mental retardation and the general mental health area.